According to Third Generation Partnership Project (3GPP) Technical Specification 25.331, a variable INTEGRITY_PROTECTION_INFO indicates the status of integrity protection in a mobile station (MS) at the radio resource control (RRC) layer. The status of integrity protection can be either “not started” or “started.” If the variable INTEGRITY_PROTECTION_INFO has the value “started,” any RRC message received by the MS will be checked for an information element (IE) “Integrity check info.” If the IE “Integrity check info” is not present, the MS shall discard the message.
According to 3GPP Technical Specification 24.008, integrity protected signaling is mandatory when a mobile station is in a UMTS connected mode with a network. There are some key exceptions, however, to the requirement that all layer 3 signaling messages be integrity protected. For example, circuit-switched (CS) domain “authentication request” and packet-switched (PS) domain “authentication & ciphering request” messages do not need to be integrity protected. Thus, these types of messages may be missing the IE “Integrity check info.”
When CS-domain and PS-domain connections between a network and a mobile station are being concurrently set-up, one domain's non-integrity-protected layer 3 message may be received at the mobile station after another domain's message initiating integrity protection. The 3GPP Technical Specification 25.331 requirement can result in an MS discarding the non-integrity-protected layer 3 message. The consequence of this discarding may results in an inability to complete a call. For example, if a CS-domain “authentication request” message (and its copies) is consistently discarded by the MS, then the call cannot complete and will eventually drop.
In other words, when a non-integrity-protected layer 3 message in one domain is received by an MS after a command to start integrity protection in another domain, the MS discards the non-integrity-protected layer 3 message. On the other hand, if the same non-integrity-protected layer 3 message in one domain was received by the MS before the command to start integrity protection in another domain, then the MS properly processes the non-integrity-protected layer 3 message. Because RRC messages (Access Stratum) and layer 3 messages (Non-Access Stratum) use different radio bearers and have different priorities, there is a real risk that a non-integrity-protected message for one domain and an integrity protection initiation message for another domain will be received out-of-order by an MS.
There is an opportunity for an MS to process out-of-order non-integrity-protected layer 3 and integrity protection initiation messages to reduce the number of dropped calls. The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Drawings and accompanying Detailed Description.